1. Filed of the Invention
This invention relates to digital display type measuring instruments, and more particularly to a digital display type measuring instrument wherein a moving displacement value of a spindle in the axial direction thereof is detected as an electric signal to be displayed digitally.
2. Description of the Prior Art
The digital display type measuring instrument, wherein a moving displacement value of a spindle of a dial gauge or the like is detected as an electric signal to be digitally displayed, is more and more popularized due to the advantages such as high resolution and easiness in reading, as compared with graduation display type measuring instruments.
The measuring instrument as described above includes: a spindle axially movably provided on a case and having mounted on one end thereof a measuring element; an encoder including a pair of scales movable relative to each other in association with a movement of this spindle, for detecting a relative moving displacement value between the pair of scales as an electric signal; and a digital displayer for digitally displaying an output from this encoder. In order to secure the measuring accuracy, it is important to keep constant a positional relationship between the both scales, and particularly, a clearance therebetween.
In the conventional construction, either one of the pair of scales is integrally fixed to the spindle and the other is fixed to the case, whereby, when a deviation of the spindle in a direction other than the axial direction thereof occurs, a clearance between the both scales fluctuates thus causing an error. For this reason, such an arrangement is adopted that, to minimize deviations of the spindle in directions other than the axial direction thereof, the spindle is penetrated through the case and the spindle is supported at opposite ends thereof by the case.
However, in the above-described arrangement, either one of the scales is fixed to an intermediate portion of the spindle positioned in the case, and further, the other of the scales should be fixed into the case, as opposed to the former scale, whereby the spindle and the two scales should be housed in the case, thus inevitably increasing the thickness of the case after all.
Even in the arrangement, wherein the opposite ends of the spindle are supported by the case, errors have occurred due to the finishing accuracy of various parts and the assembling accuracy.